Flow controller and its regulation method

ABSTRACT

The invention is intended to provide a mass flow control device incorporating a verification tank, in which the mass flow testing operations are conducted by the device itself. A mass flow control device comprises control means  18  for controlling a flow control valve mechanism based on an externally input flow set signal and a flow signal. The mass flow control device is equipped with a mass flow detector means  8  and a flow control valve mechanism  10  both of which are set in a channel  6  through which a fluid flows. The mass flow detector means  8  detects the mass flow of the fluid that flows through the channel and outputs the flow signal. The flow control valve mechanism  10  controls the mass flow by altering the valve aperture by means of valve drive signals. The mass flow control device is also equipped with a verification valve  42,  a verification tank  44  and pressure detector means  46  in the channel. The verification valve  42  opens and closes the channel. The verification tank  44  has a certain volume. The pressure detector means  46  detects the pressure of the fluid and outputs pressure detection signals. The mass flow control device is also equipped with verification control means  48  which controls the detection valve and detection tank and pressure detector means to carry out the mass flow testing operations.

TECHNICAL FIELD

The invention relates to a flow control device for measuring the flow offluids in relatively low flow levels such as gas, and in particular to aflow control device and adjustment method capable of testing flowcontrol precision.

BACKGROUND ART

Semiconductor devices such as semiconductor integrated circuits and thelike are generally produced by using several types ofsemiconductor-manufacturing devices to repeatedly carry out etching, CVDfilm formation, or the like, on semiconductor wafers or the like. Insuch cases a mass flow controlling device such as a mass flow controlleris used because of the need to precisely control the supply of traceamounts of processing gas (See Japanese Unexamined Patent Applications(Kokai) 6-119059, 7-078296, 7-134052, 7-281760, 7-306084, 11-223538, and2004-20306, U.S. Pat. No. 6,450,200, and Japanese Unexamined PatentApplications (Kokai) 8-185229 and 11-154022).

The structure of common mass flow controllers is illustrated in FIGS. 17and 18. FIG. 17 schematically illustrates the structure of an example ofa conventional mass flow controller inserted into a gas tube, and FIG.18 is a circuit diagram illustrating the flow detection means in a massflow controller.

As illustrated, the mass flow controller 2 is inserted into a flowchannel, such as a gas tube 4, through which a fluid such as a liquid orgas flows, so as to control the mass flow. A vacuum is created, forexample, in the interior of the semiconductor manufacturing deviceconnected to one end of the gas tube 4. The mass flow controller 2 has achannel 6 formed by means of stainless steel, for example, both ends ofwhich are connected to the gas tube 4. The mass flow controller 4includes mass flow detection means 8 located in the upstream stage ofthe channel 6, and a flow control valve mechanism 10 located in thedownstream stage.

The mass flow detection means 8 has a bypass group 12 comprising abundle of a plurality of bypass tubes located upstream in the directionin which the gas fluid flows in the channel 6. A sensor tube 14 isconnected to both ends of the bypass group 12 to bypass the group,allowing a smaller amount of gas fluid compared to the bypass group 12to flow at a constant rate therein. That is, a constant proportion ofgas relative to the total gas flow always flows into the sensor tube 14.A pair of control resistor wires R1 and R4 connected in series are woundaround the sensor tube 14, and flow signals S1 indicating the mass flowlevel are output by a sensor circuit 16 connected thereto.

The flow signal S1 is input to a control means 18 forming using amicro-computer, for example. The mass flow of the gas currently flowingis determined based on the flow signal S1. The flow control valvemechanism is controlled so that the determined mass flow is consistentwith the mass flow represented by an input flow set signal S0. The flowcontrol valve mechanism 10 has a flow control valve 20 located on thedownstream side of the channel 6. The flow control valve 20 has adiaphragm 22 made of bendable metal plate, for example, as a valve fordirectly controlling the mass flow of the gas fluid.

The diaphragm 22 is moved toward the valve opening 24 by beingappropriately bent and reshaped, to allow the aperture or the openingdegree of the valve opening 24 to be controlled as desired. The uppersurface of the diaphragm 22 is connected to the bottom end of anactuator 26 formed using a laminated piezoelectric element (piezoelement), thereby allowing the aperture to be adjusted in the mannerdescribed above. The actuator 26 is operated by means of the valve drivevoltage S2 output by the valve drive circuit 28 upon receiving a drivesignal from the control means 18. A sonic nozzle 29 is provided on theoutlet side of the valve opening 24, and the gas flow inlet sidepressure is set so as to be proportional to the mass flow flowingthrough the flow control valve 20. An electromagnetic actuator maysometimes be used instead of a laminated piezoelectric element as theactuator 26.

FIG. 18 illustrates the relationship between the sensor circuit 16 andthe resistor wires R1 and R4. That is, the serially connected circuitsof two reference resistors R2 and R3 are connected in parallel to theserial connection of the resistor wires R1 and R4, forming what isreferred to as a bridge circuit. A constant current source 30 for theflow of constant current is connected to the bridge circuit. Theconnecting point of the resistor wires R1 and R4 and the connectingpoint of the reference resistors R2 and R3 are connected to the inputside, for providing a differential circuit 32. The difference inpotential between the two connecting points is determined, and thedifference in potential is output in the form of a flow signal S1.

The resistor wires R1 and R4 consist of materials in which theresistance levels vary in response to temperature. The resistor wire R1is wound around the upstream side in the direction in which the gasflows, and the resistor wire R4 is wound around the downstream side.

When the gas fluid does not flow to the sensor tube 14 in the mass flowcontroller 2 constructed in the manner described above, since thetemperature of the two resistor wires R1 and R4 are the same, the bridgecircuit is in equilibrium, and the difference in potential, which is thedetected level of the differential circuit 32, is zero, for example.

When the gas fluid flows at a mass flow Q to the sensor tube 14, the gasfluid flows to the position where the resistor wire R4 on the downstreamside is wound while warmed by the heat of the resistor wire R1 locatedon the upstream side. As a result, the heat travels, causing differencesin temperature between the resistor wires R1 and R4, that is,differences in the resistance level between the two resistor wires R1and R4. The difference in potential produced by the differences in theresistance level is virtually proportional to the mass flow of the gas.A certain level of gain in the flow signal S1 thus allows the flow rateof the gas flowing at that time to be determined. The aperture of theflow control valve 20 is controlled by a PID control method, forexample, so that the gas mass flow that is detected is consistent withthe mass flow represented by the flow set signal S0 (actually, thepotential value).

In this type of mass flow controller 2, however, the actual flow in theflow control valve 20 (referred to below as “actual flow”) must beprecisely consistent with the mass flow represented by the flow setsignal (referred to below as “flow”), but when the feed gas pressurechanges, or when the device itself changes over time, etc., theapplication of valve drive voltage equal to the initial level deliveredto the device sometimes results in slight differences in the actual flowof the gas.

In view of the foregoing, the present invention was devised in order toeffectively address the above problems. An object of the invention is toprovide a flow control device and adjustment method in which flowdeviation is measured by the device itself.

The present invention relates to Japanese Patent Applications2004-182362 and 2005-153314, the details of which are herebyincorporated by reference.

SUMMARY OF THE INVENTION

The mass flow controlling device in a first aspect of the invention is amass flow control device comprising control means for controlling a flowcontrol valve mechanism based on an externally input flow set signal anda flow signal, there being inserted, in a channel through which a fluidflows, mass flow detector means for detecting the mass flow of the fluidthat flows through the channel and outputting the flow signal, and theflow control valve mechanism, which controls the mass flow by alteringthe valve aperture by means of valve drive signals, the mass flowcontrol device characterized by also comprising verification controlmeans, such that there are provided, in the channel, a verificationvalve for opening and closing the channel, a verification tank having acertain volume, and pressure detector means for detecting the pressureof the fluid and outputting pressure detection signals, the detectionvalve and detection tank and pressure detector means being used to carryout the mass flow testing operations.

In this way, the device itself is provided with a verification valve, averification tank, and the like. After the verification valve is closedto stop the supply of fluid, the changes in the pressure of the fluidflowing from the verification tank are detected, and the pressurechanges are compared to standard pressure changes, for example, makingit possible determine whether or not the mass flow of the fluid can beproperly controlled.

In this case, temperature detection means for detecting the temperatureis preferably provided near the verification tank.

The testing control means may also preferably have a standard datamemory for storing fluid pressure changes during standard measurement,and a testing data memory for storing the changes in fluid pressureduring testing.

Warning means may also preferably be connected to the testing controlmeans, and the testing control means may preferably activate the warningmeans when the test results are outside a certain range.

The testing control means may also preferably calibrate the mass flowdetection means based on the test results.

The verification tank may also preferably be inserted into the channel.

Display means for displaying the test results may also preferably beconnected to the testing control means.

A zero point measuring valve for opening and closing the channel whenmeasuring zero point may also preferably be inserted on the outlet sideof the channel.

The verification valve and zero point measuring valve may alsopreferably be provided on opposites from each other on either side ofthe mass flow control means.

At least one of either the verification valve and zero point measuringvalve may furthermore comprise a fluid storage chamber having a fluidinlet serving as a valve port and a fluid outlet, a fully closingdiaphragm that is located at the fluid inlet and that can be bent andreshaped to close the fluid inlet, and pressing means for pressing thefully closing diaphragm toward the fluid inlet.

The fully closing diaphragm may also preferably be in the form of a flatsurface or partially in the form of a spherical shell.

The pressing means may also preferably have an operating space locatedon the side opposite from the fluid storage chamber on either side ofthe fully closing diaphragm, and a valve mechanism allowing pressurizedfluid to be fed to and discharged from the operating space.

The valve mechanisms may also comprise a three-way valve.

The zero point measuring valve may also preferably be disposed at alocation facing opposite the flow control valve mechanism.

The testing control means may also measure zero point by fully closingthe verification valve and zero point measuring valve, so that the fluidis completely blocked from flowing into the channel.

The verification valve, verification tank, and pressure detection meansmay also be located farther upstream than the mass flow detection meansand flow control valve mechanism.

The verification valve may preferably be located the farthest upstreamin the channel, and the zero point measuring valve may be located thefurthest downstream.

The verification valve, verification tank, and pressure detection meansmay also be located downstream from the mass flow detection means andflow control valve mechanism.

Of the verification valve, verification tank, and pressure detectionmeans, the verification valve may be located the farthest upstream.

In one aspect of the invention, the mass flow control device testingmethod may preferably be a method comprising the steps of setting theverification flow, ensuring the stable flow of the test fluid in thechannel, detecting the pressure of the flowing fluid and the temperatureof the storage tank to determine the initial pressure and temperature,closing the verification valve to block the channel, measuring thechanges in the pressure of the fluid flowing from the verification tankafter the verification valve has been closed, and determining the testresults based on the measured pressure changes and predeterminedstandard pressure change characteristics.

In this case, the test results may preferably be displayed on displaymeans.

A warning may also be issued by the warning means when the test resultsare outside a certain permissible range.

The mass flow detection means may also be automatically calibrated basedon the test results.

The maximum and minimum standard pressure may also be predetermined inthe step for determining the test results.

The verification flow may be varied in several volumes.

A step for completely blocking the flow of the fluid in the channel tocarry out a step for measuring zero point may be done before the stepfor setting the verification flow.

At least the verification valve among the verification valve and zeropoint measuring valve may preferably be completely closed during thezero point measuring step.

The following mass flow control device testing can be done by setting upa verification valve and verification tank, etc., in the mass flowcontrol device. That is, after the verification valve is closed to stopthe supply of fluid, the changes in the pressure of the fluid flowingfrom the verification tank can be detected, and the pressure changes canbe compared to standard pressure changes, for example, allowing it to bedetermined whether or not the mass flow of the fluid can be properlycontrolled.

The following embodiment of the invention is possible. The flow controldevice is a device for controlling a flow of a fluid in a channel inwhich the fluid is supplied to a target where a pressure is lower than afluid supply source. The flow control device may be equipped with: afirst opening and closing valve for opening and closing the channel; aflow control component with a flow control valve mechanism forcontrolling the flow of the fluid flowing through the channel; apressure detector capable of detecting a pressure of the fluid on a sameside as the flow control valve mechanism relative to the first openingand closing valve; and a deviation measurement/control component forcalculating a deviation of the flow controlled by the flow controlcomponent from a standard level.

In the adjustment of the flow control device, an aperture of the flowcontrol valve mechanism is fixed. The channel is closed using a firstopening and closing valve. Then changes in a pressure of the fluid aremeasured at a predetermined first position on a same side as the flowcontrol valve mechanism relative to the first opening and closing valve.A deviation of the flow controlled by the flow control component from astandard level is calculated based on the measured pressure changes.

In this embodiment, after the flow of fluid valve is stopped at thefirst opening and closing, the fluid is allowed to pass through the flowcontrol valve to allow the deviation of the flow controlled by the flowcontrol component to be measured based on the change in pressure at thattime. It is thus possible to measure the deviation of the flowcontrolled by the flow control device set up in the line. It ispreferable that the flow control component is adjusted based on theresulting deviation from the standard level.

The various processes, from fixing the aperture of the flow controlvalve mechanism to the calculation of deviation, may preferably be donerepeatedly with varying flow control valve apertures. The flow controlcomponent may be adjusted based on the flow deviation at a plurality ofapertures obtained in these processes.

In case where the flow control component is further equipped with a flowdetector capable of measuring the flow of the fluid flowing through thechannel on the same side as the flow control valve mechanism relative tothe first opening and closing valve, and controls the flow of the fluidflowing through the channel by adjusting the aperture of the flowcontrol valve mechanism based on a target flow and the flow measured bythe flow detector, the following embodiment is preferable. That is, inadjusting the flow control component, an output level representing theflow by the flow detector is adjusted based on the deviation from thestandard level.

In this embodiment, the adjusted flow control component can properlycontrol the flow of the fluid flowing in the channel based on thestandard level and the detected flow level by the flow detectioncomponent.

In adjusting the flow control component, the following arrangement ispreferable. The channel is closed using the first opening and closingvalve, and also closed using a second opening and closing valve on aside opposite the first opening and closing valve relative to the flowdetector. The output level representing the flow by the flow detector isread in the state that the channel is closed by the first and secondopening and closing valves. Then an output level representing zero flowby the detector is adjusted. This embodiment allows the output level ofthe flow detector component to be adjusted as desired.

It is preferable that the flow control device further comprises aaccumulator in which the fluid flowing through the channel can be heldbetween the first opening and closing valve and the flow control valvemechanism. In this embodiment, the change in pressure after the firstopening and closing valve is closed is more moderate than in embodimentshaving no accumulator. It is therefore easier to measure the pressurechange accurately when adjusting the flow control device.

The deviation may preferably be calculated based on the followingmeasured levels when calculating the flow deviation from the standardlevel. That is, the deviation from the standard level may be calculatedbased on: an initial pressure PO of the fluid in the first position at afirst time in a certain time interval including a time the channel isclosed by the first opening and closing valve; an absolute temperatureT1 of the fluid in a predetermined second position on a same side as thefirst position relative to the first opening and closing valve at asecond time in the certain time interval; and a time period Δt from atime the pressure of the fluid reaches a first standard pressure at thefirst position after the channel is closed by the first opening andclosing valve until a time the pressure reaches a second standardpressure P2 which is different from the first standard pressure P1.

This embodiment allows the flow deviation per unit time of the substanceto be calculated taking into account the temperature and the pressure ofthe fluid during adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of the mass flow controldevice in the invention;

FIG. 2 illustrates the actual lay out of the various parts in the firstembodiment;

FIG. 3 illustrates a timing chart for the signals during the testoperation mode of the mass flow control device;

FIG. 4 is a flow chart of the steps involved in a standard pressurechange characteristics measurement routine;

FIG. 5 is a flow chart of the steps in a verification routine;

FIG. 6 is a graph of an example of changes in pressure signals in thestandard pressure change characteristic measurement routine andverification routine;

FIG. 7 is a block diagram of a second embodiment of the mass flowcontrol device in the invention;

FIG. 8 illustrates the actual lay out of the parts in the secondembodiment;

FIG. 9 schematically illustrates the flow control valve and zero pointmeasuring valve while attached;

FIG. 10 is a cross section of the fully closing diaphragm of the zeropoint measuring valve;

FIG. 11 is a flow chart of the flow in the zero point measuring step;

FIG. 12 illustrates a piston type actuator having a piston;

FIG. 13 is a block diagram of a third embodiment of the mass flowcontrol device in the invention;

FIG. 14 is a flow chart of the steps in the standard pressure changecharacteristic measurement routine in the third embodiment;

FIG. 15 is a flow chart of the steps in the verification routine in thethird embodiment;

FIG. 16 is a graph of examples of pressure signal S4 levels by thepressure detector means 46 respectively representing standard pressurechange characteristics and test pressure change characteristics at anaperture of 100%;

FIG. 17 is a schematic diagram of an example of a conventional mass flowcontrol device inserted into a gas tube; and

FIG. 18 is a circuit diagram illustrating the flow detection means in amass flow controller.

BEST MODE FOR IMPLEMENTING THE INVENTION

Embodiments of the mass flow control device and test method in theinvention are illustrated below with reference to the attached drawings.

First Embodiment

FIG. 1 is a block diagram of a first embodiment of the mass flow controldevice in the invention, and FIG. 2 illustrates the actual lay out ofthe various parts in the firs embodiment. Parts that are the same asthose in FIGS. 17 and 18 are designated by the same symbols and will notbe further elaborated.

As illustrated, the mass flow controller 40 is inserted into a fluidchannel, such as a gas tube 4, through which a fluid such as a liquid orgas flows, so as to adjust the mass flow (referred to below simply as“flow”). A vacuum is created, for example, in the interior of thesemiconductor manufacturing device connected to one end of the gas tube4. The mass flow controller 40 is equipped with a mass flow control mainunit 40A and a test main unit 40B for testing the mass flowcharacterized by the invention. The mass flow control main unit 40A issometimes referred to as the mass flow control component 40A below, andthe test main unit 40B is sometimes referred to as the testingcomponent. The mass flow controller 40 has a channel 6 formed ofstainless steel, for example. The fluid inlet 6A is connected to theupstream side of the gas tube 6, and the fluid outlet 6B is connected tothe downstream side of the gas tube 6.

The mass flow control component 40A is built the same as theconventional device illustrated above with reference to FIG. 17, andhas, for example, mass flow detection means 8, a flow control valvemechanism 10, and control means 18 forming using a micro-computer, forexample. The mass flow detection means 8 has bypass tubes 12, sensortube 14, sensor circuit 16, and the like. The flow signals S1 detectedusing these units are output to the control means 18. The flow controlvalve mechanism 10 has a flow control valve 20, an actuator 26 fordriving it, a valve drive circuit 28 for outputting valve drive voltageS2 to the actuator 26, and the like. The control means 18 is such thatthe aperture of the flow control valve 20 can be adjusted by a PIDcontrol method, for example, so that the flow represented by the flowset signal S0 externally input by a host computer, for example, and theflow represented by the flow signal S1 are consistent. In the examplethat is illustrated, the flow control valve mechanism 10 is set updownstream of the mass flow detection means 8, but it may also belocated upstream of the mass flow detection means 8.

The testing component 40B is located upstream of the mass flow controlcomponent 40A. The mass flow control component 40A has, in the channel6, a verification valve 42 for opening and closing the channel 6, averification tank 44 having a certain volume, pressure detecting means46 for detecting the pressure of the gas fluid and outputting pressuredetection signals, and verification control means 48 constructed using amicro-computer, for example, to carry out the mass flow testingoperations using the verification valve 42, verification tank 44, andpressure detecting means 46.

Specifically, the verification valve 42 consists of a pneumatic valve,for example, and is located farthest upstream of the channel 6 in thetesting component 40B, so that the channel 6 can be blocked as needed bybeing opened and closed by the tank valve opening and closing signalsS3, which are commands from the verification control means 48. Anactuatorless, small valve mechanism housing a three-way valve and afully closing diaphragm can be used, for example, as the pneumatic valveforming the verification valve 42.

The actuatorless, small valve mechanism bends the fully closingdiaphragm by means of operation air introduced through an operation airinlet 43 (see FIG. 2). The actuatorless small valve mechanismselectively brings about two states of the valve opening that are a fullopen state and a fully closed state that is completely sealed. Theactuatorless small valve mechanism is detachably located, in FIG. 2, inan attachment recess 47 formed in a mounting basket unit 45. Thestructure of the actuatorless small valve mechanism will be describedduring the description of the zero point measuring valve used in thesecond embodiment described below. The pressure detecting means 46 is acapacitance manometer, for example, and is such that the pressure of thegas in the channel 6 can be detected, and the detection level can beoutput in the form of a pressure signal S4 to the verification controlmeans 48.

The verification tank 44 includes a tank main unit 50 formed ofstainless steel, for example, and is located between the verificationvalve 42 and pressure detecting means 46. The tank main unit 50 has acertain volume, such as 40 cm³. A gas inlet 50A and an outlet 50B areprovided in the floor of the tank main unit 50, which are inserted intothe channel 6. The flowing gas always passes through the interior of thetank main unit 50. A platinum temperature sensor is attached astemperature detection means 51 near the tank main unit 50, specifically,in this case, on the top surface of the ceiling of the tank main unit50, so that signals indicating the detected temperature can be input tothe verification control means 48.

A standard data memory 52A for storing pressure changes serving as astandard for the gas flow (standard pressure changes) when the flow istested and a testing data memory 52B for storing changes in gas flowpressure obtained when the flow is tested are connected to theverification control means 48.

Display means 54 made of a liquid crystal display, for example, todisplay the test results and warning means 56 for issuing a warning bymeans of noise, flashing lights, or the like as needed are alsoconnected to the verification control means 48.

The verification control means 48 outputs calibration signals S10 to thesensor circuit 16 of the mass flow detection means 8 as needed, allowingthe sensor circuit 16 to be properly calibrated based on the calibrationresults. The verification control means 48 and the control means 18 ofthe mass flow control component 40A are configured to work together asneeded.

The operation of the mass flow controller of the invention constructedin the manner described above is described below.

The mass flow controller 40 has two operating modes: a normal operatingmode in which the process gas actually flows, while the flow is beingadjusted, to a semiconductor manufacturing device or the like, and atest operating mode in which mass flow test-related operations arecarried out. The test operating mode has “a standard pressure changecharacteristics measurement routine” for obtaining pressure changes thatserve as the standard, and “a test routing” for carrying out actualtesting operations.

The normal operating mode will be briefly described first. The operationis the same as was described earlier with reference to FIGS. 17 and 18.In this case, the operation of the testing component 40B is suspended.That is, the control means 18 of the mass flow control component 40Acontinuously controls the aperture of the flow control valve 20 by a PIDcontrol method, for example, so that the flow represented by the flowset signal S0 externally input by a hot computer, for example, and theflow represented by the flow signal S1 are consistent. Processing gaswith the necessary mass flow is thus provided to the downstreamsemiconductor manufacturing device or the like.

The test operating mode is described next.

In the test operating mode, the standard pressure change characteristicsmeasurement routine is employed to obtain the pressure changecharacteristics which will serve as the standard, primarily when thedevice is shipped from the factory, the device is set up in a clean roomat the shipping destination, or the like. The testing routine is carriedout periodically or non-periodically in a clean room or the like at theshipping destination to test whether or not high control flow precisionis be maintained. FIG. 3 illustrates a timing chart for the signalsduring the test operating mode of the mass flow control device. FIG. 4is a flow chart of the steps involved in the standard pressure changecharacteristics measurement routine. FIG. 5 is a flow chart of the stepsin the verification routine. FIG. 6 is a graph of an example of changesin pressure signals in the standard pressure change characteristicmeasurement routine and verification routine.

The verification routine primarily comprises the steps of: setting theverification flow; ensuring the stable flow of the test fluid (gas) inthe channel 6; detecting the pressure of the flowing fluid and thetemperature of the verification tank 44 to determine the initialpressure and temperature; closing the verification valve 42 to block thechannel 6; measuring the changes in the pressure of the fluid flowingfrom the verification tank 44 after the verification valve 42 has beenclosed; and determining the test results based on the measured pressurechanges and predetermined standard pressure change characteristics. Thestandard pressure change characteristics measurement routine fordetermining the standard pressure change characteristics will bedescribed first.

<Standard Pressure Change Characteristics Measurement Routine>

The primary steps of the standard pressure change characteristicsmeasurement routine are the same as the verification routine except forthe step comparing the pressure changes. In this case, N₂ gas is used,for example, as the fluid. As illustrated in FIGS. 1, 3, and 4, when thestandard pressure change characteristics measurement routine is begun,the verification valve 42 is open (step S1). At time t1 (see FIG. 3(A)),the flow set signal S0 is set to full scale (5V: volts) at a percentage,such as 100%, representing the maximum flow that the mass flowcontroller 40 can control (step S2). As noted above, in normal operatingmode, the flow set signal S0 is input to the control means 18 by anexternal component such as a host computer, whereas in the testoperating mode, the flow set signal is input to the control means 18from the verification control means 48, not a host computer. The controlmeans 18 thus carries out the normal flow control operation according tothe flow set signal S0 from the verification control means 48 in thesame manner as the externally input flow set signal S0. The flow setsignal S0 can generally be varied within the range of 0V to 5V, and ispreset so that 5V is 100% full scale (maximum flow).

When 5V is thus set as the flow set signal S0, the control means 18outputs valve drive voltage S2 (see FIG. 3(C)) through the valve drivecircuit 28, and controls the flow control valve 20 so that the aperturematches the flow set signal S0. As the N₂ gas thus begins to flow to thedownstream side, the mass flow at that time is detected by the mass flowdetection means 8, and the detected mass flow is input in the form of aflow signal S1 (see FIG. 3(D)) to the control means 18. The aperture iscontrolled by a PID control method as noted above so that the flowsignal S1 and flow set signal S0 are consistent with each other. At thattime, the gas flow pressure is detected by the pressure detecting means46, and the pressure signal S4 (see FIG. 3(E)) is input to theverification control means 48.

To stabilize the gas flow in this way, when a certain time such as 6seconds has elapsed (step S3), the aperture is fixed at time t2 byfixing the valve drive voltage S2 at that time to the voltage level atthat time (step S4). When the valve drive voltage S2 has thus been fixedand several seconds have elapsed, the pressure of the gas flow from thepressure detecting means 46 at that time and the tank temperature fromthe temperature detection means 51 at that time are recorded, serving asthe initial pressure MPO and initial temperature MTO ° C., respectively(step S5).

When the initial pressure and temperature have been measured andrecorded, a tank valve opening/closing signal S3 is immediately outputat time t3 to close the valve (see FIG. 3(B)), and the verificationvalve 42 is switched to a closed state (step S6). The channel 6 is thusblocked, stopping the supply of N₂ gas from the gas feed source, butbecause the tank main unit 50 of the verification tank 44 is filled withenough N₂ gas to reach a certain pressure, the N₂ gas in the tank mainunit 50 flows out downstream, resulting in a characteristics curve inwhich the flow signal S1 and pressure signal S4 decrease over time, asillustrated in FIGS. 3(D) and 3(E). A vacuum is continuously created onthe downstream side of the gas tube 4 at that time, and the aperture ofthe flow control valve 20 corresponding to the detected flow set in stepS2, that is, a flow of 100% in this case, is maintained.

Below, “an aperture corresponding to a flow of X % (based on a certainpressure)” or “an aperture representing a flow of X % (based on acertain pressure)” is also expressed as “an aperture of X %.” “Changing(or lowering) the target flow rate for the flow control valve by Y %” isalso expressed as “changing (or lowering) aperture by Y %.”

The changes in the pressure of the gas flow at this time are measured,for example, in 1 msec intervals (step S7) to obtain the pressure changecharacteristics at that time. The gas pressure is measured continuouslyuntil the gas pressure reaches a predetermined minimum level, and thegas flow is stopped when the minimum level is reached (step S8). Thistime is time t4. The pressure change data obtained above is stored asthe standard pressure change characteristics in the standard data memory52A (step S9). In this way, the standard pressure change characteristicsat the set flow of an aperture of 100% are obtained.

These standard pressure change characteristics may be preferablyacquired for a plurality of apertures. For example, the aperture (flow)may preferably be varied in 10% increments, and the standard pressurechange characteristics for each may be obtained. For example, a minimumaperture (flow) may be 10%. The detected flow setting is lowered acertain amount, such as 10%, while the detected flow setting is not atthe minimum (step S10: No). The detected flow setting is set to 90%, atthis stage (step S11). The above steps S3 through S9 are repeated untilthe aperture reaches the minimum. In this way, different standardpressure change characteristics are obtained in aperture increments of10%, and the data is all stored in the standard data memory 52A, therebycompleting the standard pressure change characteristics measurementroutine.

<Verification Routine>

The verification routine, which is implemented periodically ornon-periodically, is described next. The verification routine is carriedout, with the mass flow controller 40 incorporated in the gas feed lineof a semiconductor manufacturing device or the like in a clean room. Inthis case, N₂ gas is used as the fluid.

Steps S21 to S31 in the flow chart of FIG. 5 are the same as steps S1through S11 in the flow chart of FIG. 4, except for the difference inthe name of the pressure change data that is obtained. As such, for thesake of convenience, the timing chart in FIG. 3 used as reference forthe description of the standard pressure change characteristicsmeasurement routine will also be used as reference for the descriptionof the verification routine. However, this does not mean that thestandard pressure change characteristics measurement routine andverification routine are identical. As illustrated in FIGS. 1, 3, and 5,when the verification routine starts, the verification valve 42 is open(step S21). At time t1 (see FIG. 3(A)), the flow set signal S0 is set tofull scale (5 V: volts) at the maximum %, such as 100% such (step S22).In this test operating mode, the flow set signal S0 is output to thecontrol means 18 from the verification control means 48, not a hostcomputer. The control means 18 thus carries out the normal flow controloperation according to the flow set signal S0 from the verificationcontrol means 48 in the same manner as the externally input flow setsignal S0. As noted above, the flow set signal S0 can generally bevaried within the range of 0V to 5V, and is preset so that 5V is 100%full scale (maximum flow).

When 5V is thus set as the flow set signal S0, the control means 18outputs valve drive voltage S2 (see FIG. 3(C)) through the valve drivecircuit 28, and controls the flow control valve 20 so that the aperturematches the flow set signal S0. As the N₂ gas thus begins to flow to thedownstream side, the mass flow at that time is detected by the mass flowdetection means 8, and the detected mass flow is input in the form of aflow signal S1 (see FIG. 3(D)) to the control means 18. The aperture iscontrolled by a PID control method as noted above so that the flowsignal S1 and flow set signal S0 are consistent with each other. At thattime, the gas flow pressure is detected by the pressure detecting means46, and the pressure signal S4 (see FIG. 3(E)) is input to theverification control means 48.

To stabilize the gas flow in this way, when a certain time such as 6seconds has elapsed (step S23), the aperture is fixed at time t2 byfixing the valve drive voltage S2 at that time to the voltage level atthat time the (step S24). When the valve drive voltage S2 has thus beenfixed and several seconds have elapsed, the pressure of the gas flowfrom the pressure detecting means 46 at that time and the tanktemperature from the temperature detection means 51 at that time arerecorded, serving as the initial pressure PO and initial temperature TO° C., respectively (step S25).

When the initial pressure and temperature have been measured andrecorded, a tank valve opening/closing signal S3 is immediately outputat time t3 to close the valve (see FIG. 3(B)), and the verificationvalve 42 is switched to a closed state (step S26). The channel 6 is thusblocked, stopping the supply of N₂ gas from the gas feed source, butbecause the tank main unit 50 of the verification tank 44 is filled withenough N₂ gas to reach a certain pressure, the N₂ gas in the tank mainunit 50 flows out downstream, resulting in a characteristics curve inwhich the flow signal S1 and pressure signal S4 decrease over time, asillustrated in FIGS. 3(D) and 3(E). A vacuum is continuously created onthe downstream side of the gas tube 4 at that time, and the aperture ofthe flow control valve 20 maintains the flow detected in step S22, whichin this case is 100%.

The changes in the pressure of the gas flow at this time are measured,for example, in 1 msec intervals (step S27) to obtain the pressurechange characteristics at that time. The gas pressure is measuredcontinuously until the gas pressure reaches a predetermined minimumlevel, and the gas flow is stopped when the minimum level is reached(step S28). This time is time t4. The pressure change data obtainedabove is stored as the test pressure change characteristics in theverification data memory 52B (step S29). In this way, the standardpressure change characteristics at the set flow of an aperture of 100%are obtained.

These test pressure change characteristics may be preferably acquiredfor a plurality of apertures in the same manner as for the standardpressure change characteristics. For example, the aperture maypreferably be varied in 10% increments, and the test pressure changecharacteristics for each may be obtained. For example, a minimumaperture may be 10%. The detected flow setting is lowered a certainamount, such as 10%, while the detected flow setting is not at theminimum (step S30: No). The detected flow setting is set to 90%, at thisstage (step S31). The above steps S23 through S29 are repeated until theaperture reaches the minimum. In this way, different test pressurechange characteristics are obtained in aperture increments of 10%, andthe data is all stored in the verification data memory 52B, therebycompleting the test pressure change characteristics measurement routine.

When the test pressure change characteristics have thus been obtained,they are compared to the standard pressure change characteristics foreach aperture (each detected flow set level) to carry out the testprocess (step S32).

A way to determine the testing precision, the test results, is describedhere with reference to FIG. 6. FIG. 6 is a graph of an example ofchanges in pressure signals S4 in the standard pressure changecharacteristic measurement routine and verification routine at anaperture of 100%. The characteristics curve X0 shows the standardpressure changes at an aperture of 100%, and the characteristics curveX1 shows the test pressure change characteristics at an aperture of100%. As noted above, both characteristics curves are stored in thestandard data memory 52A and testing data memory 52B, respectively.

MΔt and Δt in relation to the predetermined pressure range from themaximum standard pressure P1 to the minimum standard pressure P2 are setin the following manner. That is, MΔt is the time it takes the pressureobtained in the standard pressure change characteristics measurementroutine to reach the minimum standard pressure P2 after reaching themaximum standard pressure P1. At is the time it takes the pressureobtained in the verification routine to reach the minimum standardpressure P2 after reaching the maximum standard pressure P1.

The detection precision at that time is represented by the followingequation.H=MΔt/Δt×PO/MPO×(273+MTO)/(273+TO)×100 (%)   (1)

MTO: initial temperature in standard pressure change characteristicsmeasurement routine

TO: initial temperature in verification routine

MPO: initial pressure in standard pressure change characteristicsmeasurement routine

PO: initial pressure in verification routine

Equation (1) is obtained in the following manner. That is, the equationof state relative to n mol ideal gas is PV=nRT. These symbols indicatethe following physical values.

P: pressure of ideal gas

V: volume of ideal gas

R: gas constant

T: absolute temperature (K)

Assuming a virtually constant volume when the pressure changes from thestandard pressure P1 to the standard pressure P2, the amount An of thesubstance flowing at that time is Δn=(P2−P1)V/RT. Here, the amount v ofthe substance per unit time is v=(P2−P1)V/(RTΔt), where Δt is the timeelapsed when the pressure changes from standard pressure P1 to standardpressure P2.

The ratio between the amount v0 of the substance per unit time in thestandard pressure change characteristics measurement routine and theamount v1 of the substance per unit time in the verification routine istherefore as follows.(v1/v0 )=MΔt(273+MTO)/Δt(273+TO)   (2)

Here, the aperture Gv of the valve for bringing about a certain flow isinversely proportional to the fluid pressure. In this embodiment, whenthe initial pressure MPO in the standard pressure change characteristicsmeasurement routine and the initial pressure PO in the test routing aredifferent, different valve apertures bring about the same target flow.In consideration of this point, the above Formula (2) becomes thefollowing Formula (3). Formula (3) is equivalent to Formula (1) relatingto the test precision H.(v1/v0)′=MΔt(273+MTO)PO/Δt(273+TO)MPO   (3)

The detection precision H is obtained in the following manner from theabove equation, assuming MΔt=17640 msec, Δt=11420 msec, MPO=0.4003210MPa (mega Pascal), PO=0.2589058 MPa, MTO=25.4° C., and TO=24.7° C.

H=100.135%

This means that when the gas flow is controlled in the same manner aswhen shipped, there is a flow error, although slight, of +0.135%.

The test process described above is repeated for each aperture todetermine the test precision H of each aperture (step S32).

When the test results are thus obtained, they are stored andsimultaneously output and displayed on display means 54, for example, toinform the operator (step S33). If needed, the mass flow detection means8 is automatically calibrated at the same time based on the test resultsso as to output the proper flow signal S1 (step S34). Flow deviationoccurs, despite the feedback control of the flow control valve 20 by thecontrol means 18 based on the flow set signal S0 and the flow signal S1,possibly because the flow signal S1 does not accurately reflect theactual flow. The calibration process can be done by adjusting the gainof the differential circuit 32 (see FIG. 18), which is an amplifier ofthe sensor circuit 16, for example.

If necessary, the test precision may be compared to a certain,predetermined permissible range, and warning means 56 can be activated,for example, when the test precision is significantly over thepermissible range to alert the operator. The verification routine iscomplete when the automatic calibration is thus concluded.

The device itself is provided with the verification valve 42 andverification tank 44. As above mentioned, after the test valve 42 hasbeen closed to stop the supply of fluid, the pressure changes in thefluid flowing out of the verification tank 44 are detected, and thepressure changes are compared to the standard pressure changes, forexample, making it possible to test whether or not the mass flow of thefluid can be properly controlled.

Because the above test operations can be conducted with the mass flowcontroller 40 incorporated as such in the gas feed system or the like ofthe semiconductor manufacturing device, the test can be done extremelyrapidly, thereby improving to that extent the operating efficiency ofthe semiconductor manufacturing device or the like.

In the above embodiment, the test was done while varying the valveaperture (detection temperature set level) in 10% increments, but is notlimited to these numerical examples. The sequence in which the pressuredetecting means 46 and verification tank 44 are disposed relative to thechannel 6 may also be reversed in terms of upstream and downstreamlocations. The inlet 50A and outlet 50B of the channel 6 were providedseparately in the tank main unit 50, but are not limited to thatarrangement. A single branched tube may be formed relative to thechannel 6, and the tank main unit 50 may be connected in the shape of a“T” to the branched tube.

The various processes described in the above embodiment may be done bydigital processing or analog processing. Particularly when done bydigital processing, the data may be discrete due to the samplingfrequency at which the various types of data are obtained, but in suchcases the data can be rounded off from the lowest digit to find pointsof agreement in the pressure data or the like in the graph illustratedin FIG. 6.

In the first embodiment, when zero point adjustment is done, theverification valve 42 is closed to stop the flow of gas in the channel 6and determine the flow signal S1 under stabilized conditions, and thezero point adjustment is done based on the resulting level.

Second Embodiment

A second embodiment of the mass flow controller of the invention isdescribed below.

The second embodiment has the function of permitting higher precisionzero point adjustment, and also affords a more compact device itself.

As deviation of the flow detection zero point, albeit slight, isunavoidable over time, the zero point is adjusted periodically ornon-periodically in this mass flow controller. The flow of the fluid(including gases and liquids) is preferably stopped completely in thedevice in order to improve the precision during zero point adjustment.In this case, where the flow control valve 20 involves the use of adiaphragm, the properties make it difficult to completely stop the flowof the fluid even when the valve is closed, as there are variousmicro-leaks, although very slight. Such leaks are not particularly aproblem when the design rules of the semiconductor manufacturing processare not all that stringent, but when the demands of finer processing,thinner films, and higher integration require more stringent designrules, such trace leaks cannot be ignored.

In the second embodiment, a more compact zero point measurement valve isprovided in order to completely eliminate extremely minute leaks. Thispoint is described below.

FIG. 7 is a block diagram of the second embodiment of the mass flowcontrol device in the invention. FIG. 8 illustrates the actual lay outof the parts in the second embodiment.

FIG. 9 schematically illustrates the flow control valve and zero pointmeasuring valve while attached. FIG. 10 is a cross section of the fullyclosing diaphragm of the zero point measuring valve. FIG. 11 is a flowchart of the flow in the zero point measuring steps.

Parts that are the same as those in FIGS. 1 and 2 are designated by thesame symbols and will not be further elaborated. The use of theactuatorless, small valve mechanism employed in the verification valve42 above will be used in the description of the zero point measurementvalve.

As illustrated in FIGS. 7 and 8, a zero point measurement valve 60 islocated the furthest downstream in the channel 6, just in front of thefluid outlet 6B. Specifically, an attachment recess 62 is provided inthe bottom surface of the mounting basket unit 45 of the mass flowcontroller (in FIG. 8), and the zero point measurement valve 60 isattached in a liquid- and air-tight manner in the attachment recess 62.The attachment recess 62 is disposed in a location facing the diaphragm22 of the flow control valve mechanism 10.

As illustrated in FIG. 9, a fluid storage chamber 64 is formed in theattachment recess 62 by more deeply excavating the mounting basket unit45. The center of the ceiling of the fluid storage chamber 64 protrudesslightly downward in FIG. 9. In this portion, a communication channel 66is formed so as to communicate with the valve port 24 on the flowcontrol valve mechanism 10 side, allowing gas that has flowed throughthe valve port 24 to flow into the fluid storage chamber 64. Thus, inrelation to the fluid storage chamber 64, the bottom end opening of thecommunication channel 66 functions as a fluid inlet 68, which is a valveport. The fluid storage chamber 64 is also provided with a fluid outlet70 through which the gas flows out. The fluid outlet 70 communicateswith the fluid outlet 6B side via a channel 72.

A ring-shaped elastic seal member 74, such as an O-ring, is providedprotruding partially downward around the fluid inlet 68 serving as thevalve port. When the valve is closed as described below, the fluid inlet68 serving as the valve port is completely closed in a liquid- orair-tight manner, completely blocking the flow of gas. A fully closingdiaphragm 76 of bendable and deformable metal is provided,compartmentalizing the bottom of the fluid storage chamber 64. Themiddle of the fully closing diaphragm 76 has a curved surface component76A formed in the shape of a downwardly convex curve, and thecircumference is fixed by being pressed by means of a fixing member 78fitted tightly into the attachment recess 62. The fixing member 78 istightened by means of screw or the like (not shown).

Here, the curved surface 76A is formed in the shape of a dome having aspherical portion, specifically, a dome having a spherical portion whichis shorter than a semi-spherical dome shape. The fully closing diaphragm76 may also be flat, without any curved portion 76A. The fixing member78 is provided with pressing means 80 for pressing the fully closingdiaphragm 76 toward the fluid inlet 68 and closing the fluid inlet 68functioning as the valve port. The pressing means 80 is formed of anoperating space 82 and a valve mechanism 84. The operating space 82 islocated on the side opposite the fluid storage chamber 64 on either sideof the fully closing diaphragm 76. The valve mechanism 84 allows apressurized fluid such as pressurized air to be supplied to anddischarged from the operating space 82. The valve mechanism 84 is drivento allow the pressurized gas to be fed to and discharged from theoperating space 82 as needed. When the pressurized gas is supplied, thefully closing diaphragm 76 having the curved portion 76A is bent andreshaped so that it can fully close the fluid inlet 68.

Under normal condition, when no pressurized gas is supplied to theoperating space 82, the fluid inlet 68 is completely open. The valve isthe normally open type valve. The valve mechanism 84 is, for example, anelectromagnetic three-way valve. The electromagnetic three-way valve canbe housed in the fixing member 78 to provide a more compact sizeoverall. In this case, a seal member 86 such as an O-ring is placedbetween the periphery of the fixing member 78 and the inner surface ofthe attachment recess 62 to prevent the compressed air in the operatingspace 82 from leaking out. An electromagnetic three-way valve can thusbe used as the valve mechanism 84, allowing compressed air that isalways compressed in one direction of the three-way valve to be suppliedto and discharged from the operating space 82 as needed. The compressedair is introduced through an 20 operating air inlet 85. Anelectromagnetic three-way valve can thus be used as the valve mechanism84, to produce a small, compact actuatorless valve mechanism as the zeropoint measurement valve 60. The operation of the zero point measurementvalve 60 is controlled by the verification control means 48.

The process for measuring the zero point of the flow sensor using thezero point measurement valve 60 constructed in the above manner isdescribed below.

The zero point measuring process may be carried out periodically ornon-periodically, but is preferably done immediately before implementingthe standard pressure change characteristics measurement routineillustrated in FIG. 4 or immediately before the measurement routineillustrated in FIG. 5.

As illustrated in FIG. 11, to implement the zero point measurementprocess, the verification valve 42 located farthest upstream in thechannel 6 and the zero point measurement valve 60 located farthestdownstream in the channel 6 are both closed to close the valves andcompletely block the flow of gas in the channel 6 (S01). That is, theflow of gas in the sensor tube 4 is completely stopped. At this time,the flow control valve 20 of the flow control valve mechanism 10 is keptopen (S02).

When the stoppage of the flow of gas in the channel 6, particularly inthe sensor tube 4, has stabilized in this state (S03) after a certaintime has passed, the flow signal S1 of the sensor circuit 16 at thattime is detected, and the detected value is stored as the zero pointdeviation level in the memory (not shown) of the control means 18 (S04).In other words, a certain output level from the verification controlmeans 48 or control means 18 measurement system (flow sensor) isestablished as electrically representing “zero flow” (offset adjustment)on the basis of the stored deviation level. In this case, as notedabove, the zero point measurement valve 60 can completely block gas(fluid) leaks, enabling highly accurate zero point measurement. At thatpoint in time, the above deviation level is stored without adjusting thezero point, and the zero point is finally adjusted, either automaticallyor by operator command, in the verification routine. That is, in S34 ofthe test routing illustrated in FIG. 5, the above zero point deviationlevel and the flow deviation level determined in the verificationroutine are automatically calibrated to adjust both the zero point andthe flow deviation. In this case, the deviation levels of the measuredresults may be displayed without the automatic calibration, and they maybe calibrated as needed upon command by the operator after viewing theresults.

In FIG. 11, when the value of the flow signal S1 is stored in S04, theflow control valve 20 shifts to the normal control state (S05), and theverification valve 42 and zero point measurement valve 60 are bothopened (S06). In the case of the standard pressure changecharacteristics measurement routine, the next step is S2 in FIG. 4 (S1is skipped), and in the case of the test routing, the next step is S22in FIG. 5 (S21 is skipped) (S07).

In the above case, as illustrated in FIG. 10, test results confirmedthat it was possible to maintain a leak-free completely closed statewithin the range complying with the following relational expression,where D is the diameter of the circle at the end surface of the curvedsurface 76A formed in the shape of a dome having a spherical portion inthe completely closing diaphragm 76, R is the radius of the sphere, P1is the pressure of compressed air, and P2 is the pressure in the fluidstorage chamber 64.2<R/D<10 (when P1−P2≧0.1 MPa)

The curved surface 76A can be partially spherical, such as asemi-spherical dome shape, but is not limited to that shape. Any curvedsurface will do, such as a shape with a dome-shaped portion having anelliptical cross section, provided that it can bring about a completelyclosed state in which the flow of gas is completely stopped. As notedpreviously, the fully closing diaphragm 76 may also have a flat shape.

A small actuatorless valve mechanism housing an electromagneticthree-way valve as the valve mechanism 84 can be used as the zero pointmeasurement valve 60 to make it more compact and save space.

Although it will depend on the design dimensions of the device, sincethe zero point measurement valve 60 is disposed opposite the flowcontrol valve mechanism 10, the communication channel 66 communicatingwith the fluid inlet 68 of the fluid storage chamber 64 and the valveport 24 opened and closed by the diaphragm 22 will have a lower volume,thus minimizing dead volume which cannot be controlled by the devicewhen gas is flowing.

As noted above, such a small actuatorless valve mechanisms can also beused for the verification valve 42 illustrated in FIG. 2.

In the second embodiment described above, a small actuatorless valvemechanism housing an electromagnetic three-way valve was used as thepressing means 80 of the zero point measurement valve 60, but it is alsopossible to use a piston actuator having a piston 90 that comes intocontact with the fully closing diaphragm 76 and presses it, as in thevariant illustrated in FIG. 12.

The zero point measurement valve 60 is located on the side opposite theverification valve 42 on either side of the bypass tube 12 and sensortube 14. Thus, when the verification valve 42 is located furtherdownstream than the bypass tube 12, for example, the zero pointmeasurement valve 60 is further upstream than the bypass tube 12.

Third Embodiment

FIG. 13 is a block diagram of a third embodiment of the mass flowcontrol device in the invention. The mass flow controller 401 in thethird embodiment differs from the mass flow controller 40 of the firstembodiment in that the testing unit 401B is downstream from the massflow control component 401A in the channel 6. The testing unit 401B ofthe mass flow controller 401 in the third embodiment differs from thetesting unit 40B of the mass flow controller 40 in the first embodimentin that the verification valve 42 is downstream of the verification tank44 and pressure detecting means 46. The structure of the mass flowcontroller 401 is otherwise the same as the mass flow controller 40 inthe first embodiment.

In the third embodiment, a vacuum is first created in the tank main unit50 by closing the upstream side flow control valve 20, resulting in areduced pressure state. The verification valve 42 is then closed, andthe flow control valve 20 is opened to a certain extent to determine howmuch the pressure in the channel 6, including the tank main unit 50,increases. The mass flow control component 401A is then tested based onthe pressure change.

<Standard Pressure Change Characteristics Measurement Routine in ThirdEmbodiment>

FIG. 14 is a flow chart of the steps in the standard pressure changecharacteristic measurement routine in the third embodiment. When thestandard pressure change characteristics are obtained, a flow set signalS0 is first set to full scale (such as 5 V) representing the maximumflow set value (100%, for example) in step S41.

In step S42, the verification valve 42 is opened, and the flow controlvalve 20 is closed. In step S43, a vacuum is created by suctioning thegas with a vacuum pump (not shown) out of the downstream fluid outlet6B, resulting in a low pressure state in the tank main unit 50 of theverification tank 44 and in the channel 6 downstream of the flow controlvalve 20.

In step S44, the control means 18 opens the flow control valve 20, andcontrols the flow control valve 20 of the flow control valve mechanism10 according to the flow set signal S0 so as to result in the flowpreviously set in step S41 (the maximum flow in this case). As a result,N₂ gas flows from the gas feed source, through the flow control valve20, channel 6, and tank main unit 50, toward the downstream vacuum pump.During the test, the flow set signal S0 is sent to the control means 18by the verification control means 48, not the host computer, just as itis in the first embodiment (see FIG. 13).

Then, in step S45, the process waits for a certain amount of time (suchas 6 seconds) until the gas flow level has stabilized. Then, in stepS46, the valve drive voltage S2 is fixed at the voltage level prevailingat that time, to fix the aperture of the flow control valve 20.

In step S47, after the flow of gas has stabilized over a certain periodof time (such as several seconds) after the aperture of the flow controlvalve 20 has been fixed, the gas flow pressure prevailing at that timeas determined by the pressure detecting means 46 is stored as theinitial pressure MPO in the standard data memory 52A. The temperature ofthe tank at that time as detected by the temperature detection means 51is stored as the initial temperature MTO in the standard data memory52A.

In step S48, the verification valve 42 is closed. As a result, the flowis blocked from the gas feed source and tank main unit 50 to thedownstream vacuum pump, and the suctioning of N₂ gas is stopped.However, because N₂ gas is then supplied from the gas fee source to thetank main unit 50, the gas flows through the flow control valve 20 andinto the channel 6 upstream from the verification valve 42, and into thetank main unit 50. As a result, the pressure increases in the channel 6upstream from the verification valve 42 and in the tank main unit 50.

In step S49, the pressure of the gas in the channel 6 is measured by thepressure detecting means 46 at certain intervals, such as every 1 msec.In step S50, it is determined whether or not the pressure of the gas inthe channel 6 has reached the pre-determined maximum limit. If thepressure of the gas in the channel 6 has not reached the maximum, theprocess returns to step S49 to continue measuring the pressure. When thepressure of the gas in the channel 6 has reached the maximum, themeasurement of the gas pressure in the channel 6 is complete.

In step S51, the resulting pressure change data (measured gas pressurevalues at each point in time) is stored as the standard pressure changecharacteristics in the standard data memory 52A in conjunction with theaperture (or the valve opening degree). In step S41, the flow set signalS0 is set to the level representing an aperture of 100%. The standardpressure change characteristics stored in the standard data memory 52Awhen the process is initially carried out in step S51 are thus thestandard pressure change characteristics an aperture of 100%.

Then, in step S52, it is determined whether or not the flow set levelrepresented by the flow set signal S0 is under the pre-determinedminimum. When step S52 is first reached, since the flow set signal S0 isset to the level representing an aperture of 100%, the result of thedetermination in step S52 is NO. The process advances to step S53.

In step S53, the aperture represented by the flow set signal S0 given tothe control means 18 is reduced in certain increments. The process thenreturns to step S42. When, for example, the aperture is reduced 10% instep S53, the pressure is determined at an aperture of 90% in thesubsequent steps S43 through S51, and the results are stored as thestandard pressure change characteristics at an aperture of 90% in thestandard data memory 52A.

When the process returns from step S53 to step S42, the pressure in thetank main unit 50 and in the channel 6 has reached the maximum (see stepS50). However, in steps S42 and S43, a vacuum is created in the tankmain unit 50 while the flow control valve 20 is closed. The pressure inthe tank main unit 50 and the channel 6 thus becomes low enough fortesting again.

The changes in pressure are then similarly measured at varyingapertures, and the standard pressure change characteristics are storedin conjunction with the apertures (set flow levels) in the standard datamemory 52A. In step S52, when it is determined that the flow set levelrepresented by the flow set signal S0 is under the minimum, the processfor obtaining the standard pressure change characteristics is complete.

<Verification Routine in Third Embodiment>

FIG. 15 is a flow chart of the steps in the verification routine in thethird embodiment. In the flow of FIG. 15, the process in steps S61through S73 are the same in principle as the process in steps S41through S53 in FIG. 14.

However, whereas the standard pressure change characteristicsmeasurement routine is carried out at the plant, for example, where themass flow controller 401 is itself produced, before the mass flowcontroller 401 is shipped from the plant, the verification routine iscarried out while the mass flow controller 401 is incorporated in thegas feed line for semiconductor-producing devices or the like. As such,the gas suctioning in steps S63 through S67 is done by a vacuum pump(not shown) connected to a semiconductor-producing device or the like(not shown) that is connected to a gas tube 4 (see FIG. 13) downstreamin the gas feed line.

In the verification routine, the data is stored in the testing datamemory 52B, not the standard data memory 52A. That is, in step S71 inFIG. 15, the pressure change data (measured gas pressure levels at eachpoint in time) is stored as test pressure change characteristics inconjunction with apertures in the testing data memory 52B. In step S67,the gas flow pressure measured by the pressure detecting means 46 aftera certain time (such as several seconds) after the aperture of the flowcontrol valve 20 has been fixed is stored as the initial pressure P0 inthe testing data memory 52B. The temperature in the tank at that time asdetected by the temperature detection means 51 is stored as the initialtemperature T0 in the testing data memory 52B.

The rest of the process in steps S61 through S73 in FIG. 15 is the sameas the process in steps S41 through S53 in FIG. 14. In the process insteps S61 through S73, the changes in pressure are measured at aplurality of apertures, and the resulting test pressure changecharacteristics in conjunction with the aperture levels are stored inthe testing data memory 52B.

FIG. 16 is a graph of examples of pressure signal S4 levels by thepressure detector means 46 representing various standard pressure changecharacteristics and test pressure change characteristics at an apertureof 100%. The characteristic curve X0 indicates standard pressure changecharacteristics at an aperture of 100% (see step S51 in FIG. 14), andthe characteristic curve X1 indicates test pressure changecharacteristics at an aperture of 100% (see step S71 in FIG. 15).

In the third embodiment, MΔt and Δt are determined as follows inrelation to the predetermined pressure range from the maximum standardpressure P1 to the minimum standard pressure P2. That is, MΔt is thetime from when the pressure obtained in the standard pressure changecharacteristics measurement routine has reached the minimum standardpressure P2 until it reaches the maximum standard pressure P1. Δt is thetime from when the pressure obtained in the verification routine hasreached the minimum standard pressure P2 until it reaches the maximumstandard pressure P1.

The test accuracy H for aperture is obtained by substituting the MΔt andΔt at the certain resulting apertures, the initial pressure MP0 andinitial temperature MT0 obtained in step S47 in FIG. 14, and the initialpressure P0 and initial temperature T0 obtained in step S67 in FIG. 15into Equation (1).

In step S74 of FIG. 15, the test accuracy H is calculated for aplurality of apertures in this manner. In step S75, the test accuracy Hfor each aperture is displayed by the display means 54. In step S76, themass flow detection means 8 is automatically calibrated based on thetest accuracy H at each aperture. The process in steps S75 and S76 isthe same as the process in steps S33 and S34 in FIG. 5.

This embodiment allows mass flow controllers to be tested whileincorporated in gas feed lines to semiconductor-producing devices andthe like.

In the above embodiments, the pressure detecting means 46 was locateddownstream of the tank main unit 50. However, the pressure detectingmeans 46 may be located upstream of the tank main unit 50 and/or flowcontrol valve 20, and the pressure in the channel 6 can be detected atthose locations. In another possible embodiment, the pressure detectingmeans 46 can detect the pressure in the tank main unit 50. That is, thepressure detection means may be located on the same side as the flowcontrol valve for controlling the mass flow of the fluid flowing in thechannel, relative to the verification valve component for closing thechannel, and can detect the pressure of the fluid in the channel,including the tank main unit. However, the pressure detection means ispreferably located between the test valve component and the flow controlvalve.

In the above embodiments, the temperature detection means 51 was locatedin the tank main unit 50. However, the temperature detection means 51may be located upstream of the tank main unit 50 and/or flow controlvalve 20, and the temperature of the fluid in the channel 6 can bedetected at those locations. In another possible embodiment, thetemperature detecting means 51 can be located downstream of the tankmain unit 50 and/or flow control valve 20, and the temperature of thefluid in the channel 6 can be detected at those locations. That is, thetemperature detection means may be located on the same side as the flowcontrol valve for controlling the mass flow of the fluid flowing in thechannel, relative to the verification valve component for closing thechannel, and can detect the temperature of the fluid in the channel,including the tank main unit, in those locations.

In the above embodiments, the tank main unit 50 was provided instainless steel, and the gas inlet 50A and outlet 50B connected to thechannel 6 were provided in its floor. However, the tank can have anotherstructure. For example, the channel can be provided with a componenthaving a cross sectional area that is greater than other parts and isperpendicular to the direction of the gas flow, and this portion can beused as a tank. Instead of a tank, a plurality of curved components canbe provided in the channel connecting the test valve that closes thechannel and the flow control valve for controlling the mass flow of thefluid flowing through the channel. The plurality of curved componentsprovide a channel that is longer than when the flow control valve andtest valve are linearly linked. This portion can be used instead of atank. That is, the flow controller can have a structure in which thefluid is collected between the test valve and flow control valve.

In the above embodiments, the initial pressure levels MP0 and P0, andthe initial temperatures MT0 and T0, were the pressure and temperaturewhen the test valve 42 was closed. However, the initial pressure andtemperature used in the test may be the fluid pressure and temperatureat other points in time. For example, the initial pressure andtemperature used in the test may be the pressure and temperature at apoint in time after a predetermined period of time has passed after thetest valve 42 is closed. They may also be the temperature and pressureat a certain predetermined retroactive period of time from the point intime at which the test valve 42 is closed. That is, the initial pressureand temperature used in the test can be temperatures and pressure levelsat points in time included in certain time divisions, including pointsin time when the channel is closed by the test valve.

The present invention was described in detail above with reference topreferred illustrated embodiments. However, the invention is not limitedto the structures and embodiments described above. The inventionincludes various modifications and equivalent structures. Moreover,although the various elements of the invention which have been disclosedwere disclosed in various combinations and structures, those areillustrations, and the elements may be more or fewer. The elements mayalso be a single element. Such embodiments are included within the scopeof the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to devices for supplying properamounts of gas to a target device used while maintaining the interior atlow pressure, such as various semiconductor manufacturing devicesinvolving CVD film-forming, etching, and the like.

1. A flow control device for controlling a flow of a fluid in a channelin which the fluid is supplied to a target where a pressure is lowerthan a fluid supply source, comprising: a first opening and closingvalve for opening and closing the channel; a flow control component witha flow control valve mechanism for controlling the flow of the fluidflowing through the channel; a pressure detector capable of detecting apressure of the fluid on a same side as the flow control valve mechanismrelative to the first opening and closing valve; and a deviationmeasurement/control component for calculating a deviation of the flowcontrolled by the flow control component from a standard level, whereinthe deviation measurement/control component fixes an aperture of theflow control valve mechanism and measures changes in the pressure usingthe pressure detector while the channel is closed by the first openingand closing valve, and calculates the deviation from the standard levelbased on the measured changes in the pressure.
 2. A flow control devicein accordance with claim 1, wherein the flow control component furthercomprises a flow detector capable of measuring the flow of the fluidflowing through the channel on the same side as the flow control valvemechanism relative to the first opening and closing valve, and controlsthe flow of the fluid flowing through the channel by adjusting theaperture of the flow control valve mechanism based on a target flow andthe flow measured by the flow detector, and the deviationmeasurement/control component is capable of adjusting an output levelrepresenting the flow by the flow detector based on the deviation fromthe standard level.
 3. A flow control device in accordance with claim 2,further comprising a second opening and closing valve for opening andclosing the channel on a side opposite the first opening and closingvalve relative to the flow detector, wherein the deviationmeasurement/control component is capable of reading the output levelrepresenting the flow by the flow detector while the channel is closedby the first and second opening and closing valves, and adjusting anoutput level representing zero flow by the detector.
 4. A flow controldevice in accordance with claim 1, further comprising a accumulator inwhich the fluid flowing through the channel can be held between thefirst opening and closing valve and the flow control valve mechanism. 5.A flow control device in accordance with claim 1, further comprising atemperature detector capable of measuring a temperature of the fluid onthe same side as the flow control valve mechanism relative to the firstopening and closing valve, wherein the deviation measurement/controlcomponent further calculates the deviation from the standard level basedon: an initial pressure PO of the fluid at a first time in a certaintime interval including a time the channel is closed by the firstopening and closing valve, an absolute temperature T1 of the fluid at asecond time period in the certain time interval, and a time period Δtfrom a time the pressure of the fluid reaches a certain first standardpressure P1 after the channel is closed by the first opening and closingvalve until a time the pressure reaches a certain second standardpressure P2 which is different from the first standard pressure P1.
 6. Aflow control device in accordance with claim 5, wherein the deviationmeasurement/control component calculates the deviation from the standardlevel based on a ratio between PO/(T1×Δt) and a certain constant relatedto the standard level.
 7. A mass flow control device comprising a flowcontrol component which has in a channel through which a fluid flows: aflow detector for detecting a mass flow of the fluid that flows throughthe channel and outputting a flow signal; and a flow control valvemechanism for controlling the mass flow by altering a valve aperture bymeans of valve drive signals, and controls the flow control valvemechanism based on an externally input flow set signal and the flowsignal, wherein the mass flow control device comprises a deviationmeasurement/control component which has in the channel: a first openingand closing valve for opening and closing the channel; a accumulatorhaving a certain volume; and a pressure detector for detecting apressure of the fluid and outputting a pressure detection signal, andcontrolling the first opening and closing valve and the accumulator andthe pressure detector to perform a mass flow test operations.
 8. A massflow control device in accordance with claim 7, wherein the deviationmeasurement/control component calibrates the flow detector based on aresult of the test.
 9. A mass flow control device in accordance withclaim 7, wherein a second opening and closing valve for opening andclosing an outlet side of the channel during a zero point measurement isexecuted is provided in the channel.
 10. A mass flow control device inaccordance with claim 7, wherein the first opening and closing valve,the accumulator, and the pressure detector are provided further upstreamthan the flow detector and the flow control valve mechanism.
 11. A massflow control device in accordance with claim 7, wherein the firstopening and closing valve, the accumulator, and the pressure detectorare provided further downstream than the flow detector and the flowcontrol valve mechanism.
 12. A method for adjusting a flow controldevice that controls a flow of a fluid in a channel in which the fluidis supplied to a target where a pressure is lower than a fluid supplysource, the flow control device comprising a flow control component witha flow control valve mechanism for controlling the flow of the fluidflowing through the channel, the adjusting method comprising the stepsof: a) fixing an aperture of the flow control valve mechanism; b)closing the channel using a first opening and closing valve; c)measuring changes in a pressure of the fluid at a predetermined firstposition on a same side as the flow control valve mechanism relative tothe first opening and closing valve after the steps a) and b); d)calculating a deviation of the flow controlled by the flow controlcomponent from a standard level based on the measured pressure changes;and e) adjusting the flow control component based on the deviation fromthe standard level.
 13. A method in accordance with claim 12, whereinthe flow control component further comprises a flow detector capable ofmeasuring the flow of the fluid flowing through the channel on the sameside as the flow control valve mechanism relative to the first openingand closing valve, and controls the flow of the fluid flowing throughthe channel by adjusting the aperture of the flow control valvemechanism based on a target flow and the flow measured by the flowdetector, the step e) comprising the step of adjusting an output levelrepresenting the flow by the flow detector based on the deviation fromthe standard level.
 14. A method in accordance with claim 13, furthercomprising the steps of: f) closing the channel using the first openingand closing valve, and closing the channel using a second opening andclosing valve on a side opposite the first opening and closing valverelative to the flow detector; g) reading the output level representingthe flow by the flow detector while the channel is closed by the firstand second opening and closing valves; and h) adjusting an output levelrepresenting zero flow by the detector.
 15. A method in accordance withclaim 12, wherein the step d) further comprises the step of calculatingthe deviation from the standard level based on: an initial pressure POof the fluid in the first position at a first time in a certain timeinterval including a time the channel is closed by the first opening andclosing valve; an absolute temperature T1 of the fluid in apredetermined second position on a same side as the first positionrelative to the first opening and closing valve at a second time in thecertain time interval; and a time period Δt from a time the pressure ofthe fluid reaches a first standard pressure P1 at the first positionafter the channel is closed by the first opening and closing valve untila time the pressure reaches a second standard pressure P2 which isdifferent from the first standard pressure P1.
 16. A method inaccordance with claim 15, wherein the step d) further comprises the stepof calculating the deviation from the standard level based on a ratiobetween PO/(T1×Δt) and a certain constant related to the standard level.17. A method for testing a mass flow control device, wherein the massflow control device comprises: a flow control component which has in achannel through which a fluid flows: a flow detector for detecting amass flow of a fluid that flows through the channel and outputting aflow signal; and a flow control valve mechanism for controlling the massflow by altering a valve aperture by means of valve drive signals, andcontrols the flow control valve mechanism based on an externally inputflow set signal and the flow signal; and a deviation measurement/controlcomponent which has in the channel: a first opening and closing valvefor opening and closing the channel; a accumulator having a certainvolume; and a pressure detector for detecting a pressure of the fluidand outputting a pressure detection signal, and controls the firstopening and closing valve and the accumulator and the pressure detectorto perform a mass flow test operation, and the testing method comprisesthe steps of: setting a verification flow; ensuring a stable flow of afluid for the test in the channel; detecting a pressure of the flowingfluid and a temperature of the accumulator to determine an initialpressure and an initial temperature respectively; and closing thechannel using the first opening and closing valve; measuring changes ina pressure of a fluid flowing from the accumulator after the closure ofthe channel; and determining a test results based on the measuredpressure changes and a predetermined standard pressure changecharacteristic.
 18. A method for testing a mass flow control device inaccordance with claim 17, further comprising calibrating the flowdetector automatically based on the test results.
 19. A method fortesting a mass flow control device in accordance with claim 17, furthercomprising altering the verification flow in various amounts.
 20. Amethod for testing a mass flow control device in accordance with claim17, further comprising, before the step for setting the verificationflow, measuring a zero point by blocking the flow of the fluid flowingin the channel.